Audacity as shipped does not import MP4. The manual's Importing Audio page lists exactly what the program reads with no extra libraries installed, and MP4 is not on that list. Depending on the file type filter you picked in the dialog, the file may not even be selectable — the manual says that choice "filters the list of files in the window by restricting it to files of that type."
The standard answer everywhere is "install FFmpeg." That is what the manual says too — except on one platform, where Audacity's own FAQ page adds a parenthetical that the Importing Audio page leaves out.
What Audacity reads without FFmpeg
From the Importing Audio page, verbatim:
"The audio formats importable by Audacity with the File > Import > Audio command, as shipped are:"
"For uncompressed audio: most WAV and AIFF files including all PCM variants can be imported into Audacity"
"Compressed audio: MP3, Ogg Vorbis, FLAC and MP2 can be imported into Audacity."
MP4 sits in the other list on the same page — the one that needs an optional library:
"You can install the optional FFmpeg library to import a much larger range of audio formats including AC3, M4A, MP4 and WMA (if the files are not DRM-protected to work only in particular software). FFmpeg will also import audio from most video files or DVDs that are not DRM-protected."
Note the wording in that last sentence: audio from video files. The manual describes pulling the soundtrack out, not opening the picture.
FFmpeg is optional for a reason that has nothing to do with your machine. The FFmpeg FAQ page states it directly: "Because of software patents, Audacity cannot include the FFmpeg software or distribute it from its own websites." That page points installation details at the Audacity Support site rather than spelling them out, so for the actual download and setup steps, check the official documentation.
The exception the forum threads miss
The FAQ page "Opening and Saving Files" writes the same sentence with an extra clause:
"You can install the optional FFmpeg library to import and export a much larger range of audio formats including AC3, M4A, MP4 and WMA (on Mac only, Audacity can import unprotected M4A, MP4 and MOV files without FFmpeg)."
Two qualifiers in that parenthesis, and neither survives being paraphrased:
- Mac only. It says nothing about Windows or Linux.
- Unprotected. DRM-protected files are excluded, which the page treats separately (below).
The version of that sentence on the Importing Audio page does not carry the parenthesis. So whether you are told to install anything depends on which of the two official pages you land on first — and the forum threads that get ranked for this problem are working from the shorter version.
Practical consequence: if you are on a Mac with an unprotected MP4, try the import before you install anything.
If you are on Windows or Linux
You have two routes, and they solve different problems.
Route 1 — install the optional FFmpeg library. This is the manual's own answer, and it is the right one if you will keep opening M4A, AC3, WMA and video files in Audacity. Get the steps from the official Audacity Support documentation, not from a blog post with a version number in it.
Route 2 — hand Audacity a format it already reads. Pull the audio track out of the MP4 first and import that instead. WAV, AIFF, MP3, Ogg Vorbis, FLAC and MP2 are all on the shipped list above, so nothing extra has to be installed on any platform.
Try it right here
Runs in your browser. Your file is not uploaded anywhere.
That runs inside this browser tab — the MP4 is read from disk, the audio track is written out locally, and nothing is uploaded. Drop the result into Audacity with File > Import > Audio. If you want the conversion knobs rather than a preset, extract audio from video is the full tool; for iTunes-style audio files that are already separate from any video, M4A to MP3 is the shorter path.
It still fails after installing FFmpeg
This is the case that sends people back to the forums, and the manual explains it in a place nobody reads: which importer gets first attempt depends on how you opened the file.
From the Importing Audio page:
"The file type choice determines which importer attempts the file first when using the Open or Import Audio dialogs. For example, a WAV file could be imported by Audacity's native WAV importer or by the optional FFmpeg library if this was installed."
From the Import Filtering and Importer Order page:
"All files: All files in the list are selectable, even those not supported by Audacity or FFmpeg; The built-in Audacity importers will be tried first, then FFmpeg (if installed)"
"FFmpeg compatible files - this option is only available if you have installed the optional FFmpeg extension."
That second line doubles as a free diagnostic: if "FFmpeg compatible files" is missing from the file type dropdown, FFmpeg is not installed — whatever the installer told you.
Now the part that explains the "it worked yesterday" reports. The Extended Import Preferences page:
"If using File > Recent Files or dragging in audio files, "Attempt to use filter in OpenFile dialog first" has no effect; Audacity will always try first the default importer for the file type, unless a rule is set that asks for another importer to be tried first."
Dragging a file in is not the same operation as importing it through the dialog. The manual spells out what drag-and-drop maps to: dropping files into an open project window "is equivalent to File > Import > Audio", while dropping them onto the Audacity icon "is equivalent to File > Open". Either way, the file type filter you carefully set in the dialog is not part of the transaction.
So: use File > Import > Audio and set the file type dropdown explicitly. If you want the choice to stick, the manual documents rules in Extended Import Preferences — its worked example, written for malformed MP3s, has you type a pattern in the "File Extensions" column, drag "FFmpeg compatible files" to the top of the "Importer order" column, and de-select "Attempt to use filter in OpenFile dialog first."
Two other causes worth ruling out
The file is DRM-protected. Both of the pages quoted above exclude protected files, and the FAQ gives the official workaround: "If an audio file you want to import is DRM-protected (for example, an older iTunes M4P file), first burn it to an audio CD in the application that is licensed to play it. Then rip the CD track to WAV or AIFF."
The file is damaged. Audacity has a distinct message for that case. The manual introduces it as: "The following two warning messages occur when you try to open or import a corrupted file." The two messages are "Project file or audio file could not be opened - probably corrupt." and "Audio file or Project file could not be imported - probably corrupt." If you see that wording, no importer change will help — the input is the problem.
How to tell it worked
A new track appears, and the Track Control Panel tells you what you got. Two documented behaviours to expect: "Audacity always imports files at their original sample rate, as displayed in the Track Information Area of the Track Control Panel", and the bit depth follows your preference, not the file — "This setting defaults to 32-bit float. Therefore by default an imported file will show in the Track Control Panel as 32-bit float, even if its original bit depth is lower."
A track showing 32-bit float is not a sign that something re-encoded your audio behind your back. That is the documented default.
FAQ
Do I need FFmpeg to import MP4 into Audacity? On Windows and Linux, the manual's route for MP4 is the optional FFmpeg library. On Mac, the FAQ page adds that Audacity "can import unprotected M4A, MP4 and MOV files without FFmpeg" — Mac only, and only for unprotected files.
Can Audacity open the video inside an MP4? The manual describes FFmpeg as importing "audio from most video files or DVDs that are not DRM-protected." That sentence is about the audio. For anything beyond that, check the official documentation.
Why does drag-and-drop fail when File > Import > Audio works? Because the file type filter only applies to the dialogs. The manual states that when dragging files in, "Attempt to use filter in OpenFile dialog first" has no effect and the default importer for the file type is tried first, unless you have set a rule.
Can I just convert the MP4 to MP3 and import that? Yes — the Importing Audio page lists MP3 among the formats importable as shipped. Worth knowing if you are comparing sources: the FAQ page's list of shipped formats reads "Compressed audio formats: Ogg Vorbis, FLAC and MP2" and does not include MP3, so the two official pages read differently on this point.
Nothing works and I only need the audio once. Extract the track in the browser and skip the library question entirely. See all Clapr tools, or the rest of the fix guides — the same importer-versus-container confusion shows up in CapCut refusing an MP4.
Quotations from the Audacity Manual pages Importing Audio, FAQ: Opening and Saving Files, Import Filtering and Importer Order, Extended Import Preferences and Error: Opening or reading file, checked 16 September 2026.
